U.S. patent application number 11/744614 was filed with the patent office on 2007-11-01 for treating biological tissues to mitigate post-implantation calcification.
Invention is credited to Alain F. Carpentier, Sophie Carpentier, Crystal M. Cunanan, Michael N. Helmus, Christine Loshbaugh, Lillian J. Quintero, H. Chris Sarner.
Application Number | 20070255423 11/744614 |
Document ID | / |
Family ID | 22564201 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070255423 |
Kind Code |
A1 |
Carpentier; Alain F. ; et
al. |
November 1, 2007 |
TREATING BIOLOGICAL TISSUES TO MITIGATE POST-IMPLANTATION
CALCIFICATION
Abstract
A method for fixation of biological tissues, and bioprosthetic
devices prepared by such method. The method generally comprises the
steps of A) fixing the tissue, B) treating the tissue with a
mixture of i) a denaturant, ii) a surfactant and iii) a
crosslinking agent, C) fabricating or forming the bioprosthesis
(e.g., forming the tissue and attaching any non-biological
components thereto) and D) subjecting the bioprosthesis to terminal
sterilization.
Inventors: |
Carpentier; Alain F.;
(Paris, FR) ; Carpentier; Sophie; (Paris, FR)
; Cunanan; Crystal M.; (Mission Viejo, CA) ;
Quintero; Lillian J.; (Chester, NJ) ; Helmus; Michael
N.; (Worcester, MA) ; Loshbaugh; Christine;
(Irvine, CA) ; Sarner; H. Chris; (Laguna Hills,
CA) |
Correspondence
Address: |
EDWARDS LIFESCIENCES CORPORATION
LEGAL DEPARTMENT
ONE EDWARDS WAY
IRVINE
CA
92614
US
|
Family ID: |
22564201 |
Appl. No.: |
11/744614 |
Filed: |
May 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10345120 |
Jan 14, 2003 |
7214344 |
|
|
11744614 |
May 4, 2007 |
|
|
|
09828650 |
Apr 6, 2001 |
6547827 |
|
|
10345120 |
Jan 14, 2003 |
|
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|
09157546 |
Sep 21, 1998 |
6214054 |
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09828650 |
Apr 6, 2001 |
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Current U.S.
Class: |
623/23.72 |
Current CPC
Class: |
Y10S 623/917 20130101;
A61L 2430/40 20130101; Y10S 623/901 20130101; A61L 27/3641
20130101; Y10S 623/915 20130101; A61L 27/3687 20130101; A61L 33/12
20130101; A61L 27/3683 20130101; A61P 19/00 20180101; Y10S 623/92
20130101; A61L 2400/02 20130101; A61L 2/0088 20130101; A61L 27/3645
20130101; A61L 27/3691 20130101; A61L 27/3604 20130101 |
Class at
Publication: |
623/023.72 |
International
Class: |
A61F 2/02 20060101
A61F002/02 |
Claims
1. A method for treating biological tissue which contains
connective tissue protein to reduce the potential for
post-implantation calcification and thrombogenicity, said method
comprising the steps of: a. crosslinking the connective tissue
protein within the biological tissue with a crosslinking agent; b.
after crosslinking, immersing the biological tissue in a first
solution containing a crosslinking agent and heating the first
solution to a temperature of about 50.degree. C. for a first period
of time; then c. assembling the bioprosthesis by attaching any
non-biological components of the prosthesis to the biological
tissue; and, d. subjecting the bioprosthesis to a sterilant by
immersing the bioprosthesis in a sterilizing solution containing
glutaraldehyde and heating the second solution to a temperature of
37.5.+-.2.5.degree. C. for a sterilizing period of time.
2. The method of claim 1, wherein the first period of time is
between 2 to 24 hours.
3. The method of claim 1, wherein the first solution contains a
mixture of the crosslinking agent, a denaturing agent and a
surfactant.
4. The method of claim 1, wherein the crosslinking agent of the
first solution is glutaraldehyde.
5. The method of claim 1, wherein the sterilizing period of time is
between 1-6 days.
6. The method of claim 1, further including, between the steps of
crosslinking and immersing the biological tissue in the first
solution, immersing the biological tissue in a second solution
containing a mixture of a crosslinking agent, a denaturing agent
and a surfactant.
7. The method of claim 1, wherein the biological tissue is
pericardium and the bioprosthesis is a heart valve.
8. The method of claim 1, wherein the step of subjecting the
bioprosthesis to a sterilant is carried out in a sealed container
and the method further comprises storing the bioprosthesis within
the sealed container.
9. A method for treating biological tissue which contains
connective tissue protein to reduce the potential for
post-implantation calcification and thrombogenicity, said method
comprising the steps of: crosslinking the connective tissue protein
within the biological tissue with glutaraldehyde; then, immersing
the biological tissue in a first solution containing glutaraldehyde
and heating the first solution to a temperature of about 50.degree.
C. for a first period of time; then, immersing the biological
tissue in a second solution containing a mixture of a crosslinking
agent, a denaturing agent and a surfactant; and then, immersing the
biological tissue in a sterilizing solution containing
glutaraldehyde and heating the sterilizing solution to a
temperature of 37.5.+-.2.5.degree. C. for a sterilizing period of
time.
10. The method of claim 9, wherein the first period of time is
between 2 to 24 hours.
11. The method of claim 9, wherein the first solution contains a
mixture of the glutaraldehyde, a denaturing agent and a
surfactant.
12. The method of claim 9, wherein the second solution contains a
mixture of formaldehyde, ethanol and Tween-80.
13. The method of claim 9, wherein the sterilizing period of time
is between 1-6 days.
14. The method of claim 9, wherein the biological tissue is
pericardium and the method further includes forming a heart valve
from the treated pericardium.
15. A method for fabricating a bioprosthetic heart valve to reduce
the potential for post-implantation calcification and
thrombogenicity, said method comprising the steps of: crosslinking
pericardial tissue with glutaraldehyde; immersing the pericardial
tissue in a first solution containing glutaraldehyde and heating
the first solution to a temperature of about 50.degree. C. for a
first period of time; immersing the pericardial tissue in a second
solution containing a mixture of a crosslinking agent, a denaturing
agent and a surfactant; assembling a bioprosthetic heart valve by
attaching any non-biological components of the heart valve to the
pericardial tissue; and, immersing the bioprosthetic heart valve in
a sterilizing solution containing glutaraldehyde and heating the
sterilizing solution to a temperature of 37.5.+-.2.5.degree. C. for
a sterilizing period of time.
16. The method of claim 15, wherein the first period of time is
between 2 to 24 hours.
17. The method of claim 15, wherein the first solution contains a
mixture of the glutaraldehyde, a denaturing agent and a
surfactant.
18. The method of claim 15, wherein the second solution contains a
mixture of formaldehyde, ethanol and Tween-80.
19. The method of claim 15, wherein the sterilizing period of time
is between 1-6 days.
20. The method of claim 15, wherein the step of immersing the
bioprosthetic heart valve in a sterilizing solution is carried out
in a sealed container and the method further comprises storing the
bioprosthetic heart valve within the sealed container.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/345,120, filed Jan. 14, 2003, which is
continuation of U.S. patent application Ser. No. 09/828,650, filed
Apr. 6, 2001, now U.S. Pat. No. 6,547,827 which is a continuation
of U.S. patent application Ser. No. 09/157,546, filed Sep. 21,
1998, now U.S. Pat. No. 6,214,054, the disclosures of which are
incorporated fully herein by reference.
FIELD OF THE INVENTION
[0002] The invention pertains generally to medical method/devices
and more particularly to a method for fixing (e.g., tanning or
crosslinking) and sterilizing biological tissue to I) decrease the
fixed tissue's propensity for post-implantation calcification and
ii) decrease the thrombogenicity of the fixed tissue.
BACKGROUND OF THE INVENTION
[0003] Various types of implantable medical devices may be formed
wholly or partially of biological tissue that has been chemically
"fixed" or preserved. The technique used for chemical fixation of
biological tissues typically requires exposure of the biological
tissue to one or more chemical agents that are capable of forming
cross-linkages between connective tissue protein molecules present
in the tissue.
[0004] Examples of fixed biological tissues that have been used to
form implantable bioprostheses include cardiac valves, blood
vessels, skin, dura mater, pericardium, ligaments and tendons.
These biological tissues typically contain connective tissue
proteins (i.e., collagen and elastin) which act as the supportive
framework of the tissue. The pliability or rigidity of each
biological tissue is largely determined by the relative amounts of
collagen and elastin present within the tissue and/or by the
physical structure and confirmation of its connective tissue frame
work.
[0005] Each Collagen molecule is made up of three (3) polypeptide
chains intertwined in a coiled helical confirmation. The Chemical
fixatives (i.e., tanning agents) which are used to preserve
biological tissues generally form chemical cross-linkages between
the polypeptide chains within a given collagen molecule (i.e.,
intramolecular crosslinkages), or between adjacent collagen
molecules (i.e., intermolecular crosslinkages).
[0006] Examples of chemical fixative agents which have been
utilized to cross-link collagenous biological tissues include;
aldehydes (e.g., formaldehyde, glutaraldehyde, dialdehyde starch,
para formaldehyde, glyceroaldehyde, glyoxal acetaldehyde,
acrolein), diisocyanates (e.g., hexamethylene diisocyanate),
carbodiimides, photooxidation, and certain polyepoxy compounds
(e.g., Denacol-810, -512, or related compounds). Of the various
chemical fixatives available, glutaraldehyde is the most widely
used. Glutaraldehyde is used as the fixative for many commercially
available bioprosthetic products, such as porcine bioprosthetic
heart valves (i.e., the Carpentier-Edwards.RTM. stented porcine
bioprosthesis; Baxter Healthcare Corporation; Edwards CVS Division,
Irvine, Calif. 92714-5686), bovine pericardial heart valve
prostheses (e.g., Carpentier-Edwards.RTM. Pericardial
Bioprosthesis, Baxter Healthcare Corporation, Edwards CVS Division;
Irvine, Calif. 92714-5686) and stentless porcine aortic prostheses
(e.g., Edwards.RTM. PRIMA.quadrature. Stentless Aortic
Bioprosthesis, Baxter Edwards AG, Spierstrasse 5, GH6048, Horn,
Switzerland).
[0007] One problem which has been associated with the implantation
of bioprosthetic materials is that the connective tissue proteins
(i.e., collagen and elastin) within these materials can become
calcified following implantation within the body. Such
calcification can result in undesirable stiffening or degradation
of the bioprosthesis. Two (2) types of calcification--intrinsic and
extrinsic--are known to occur in fixed collagenous bioprostheses,
although the exact mechanism(s) by which such calcification occurs
is unknown. Intrinsic calcification is characterized by the
precipitation of calcium and phosphate ions within the fixed
bioprosthetic tissue, including the collagen matrix and remnant
cells. Extrinsic calcification is characterized by the
precipitation of calcium and phosphate ions within the thrombus,
including adherent cells (e.g., platelets) to the bioprosthesis and
the development of calcium phosphate-containing surface plaques on
the bioprosthesis.
[0008] The factors that affect the rate at which fixed tissue
bioprostheses undergo calcification have not been fully elucidated.
However, factors that are thought to influence the rate of
calcification include: [0009] a) patient's age; [0010] b) existing
metabolic disorders (i.e., [0011] c) hypercalcemia, diabetes,
etc.); [0012] d) dietary factors; [0013] e) infection; [0014] f)
parenteral calcium administration; [0015] g) dehydration; [0016] h)
distortion/mechanical factors; [0017] i) inadequate coagulation
therapy during initial period following surgical implantation; and
[0018] j) host tissue responses.
[0019] The factors that are thought to affect the propensity for
platelets to adhere to a fixed bioprosthetic tissue include: [0020]
a) tissue damage; [0021] b) diet; [0022] c) surface properties of
the tissue, including the nature of exposed collagen (e.g., type I,
IV, etc.); [0023] d) metabolic changes; [0024] e) coagulation;
[0025] f) hemodynamics [0026] g) inflammation; and, [0027] h)
infection.
[0028] Various techniques have heretofore been proposed for
mitigating the in situ calcification of glutaraldehyde-fixed
bioprostheses. Included among these calcification mitigating
techniques are the methods described in U.S. Pat. No. 4,885,005
(Nashef et al.) entitled Surfactant Treatment of Implantable
Biological Tissue To Inhibit Calcification; U.S. Pat. No. 4,648,881
(Carpentier et al.) entitled Implantable Biological Tissue and
Process For Preparation Thereof; U.S. Pat. No. 4,976,733 (Girardot)
entitled Prevention of Prosthesis Calcification; U.S. Pat. No.
4,120,649 (Schechter) entitled Transplants; U.S. Pat. No.
5,002,2566 (Carpentier) entitled Calcification Mitigation of
Bioprosthetic Implants; EP 103947A2 (Pollock et al.) entitled
Method For Inhibiting Mineralization of Natural Tissue During
Implantation and WO84/01879 (Nashef et al.) entitled Surfactant
Treatment of Implantable Biological Tissue to Inhibit
Calcification; and, in Yi, D., Liu, W., Yang, J., Wang, B., Dong,
G., and Tan, H.; Study of Calcification Mechanism and
Anti-calcification On Cardiac Bioprostheses Pgs. 17-22, Proceedings
of Chinese Tissue Valve Conference, Beijing, China, June 1995.
[0029] There presently remains a need in the art for the
development of new calcification-mitigating methods for fixing
(i.e., tanning and crosslinking) and sterilizing biological tissues
to provide bioprosthetic devices which are a) less likely to become
calcified and b) less thrombogenic, following implantation within a
patient's body.
SUMMARY OF THE INVENTION
[0030] Broadly stated, the present invention provides a method for
chemical fixation and sterilization of biological tissue,
comprising the steps of: [0031] 1. HARVEST/PREPARATION OF
TISSUE--harvesting and preparing a biological tissue. [0032] 2.
FIXATION OF TISSUE--contacting the biological tissue with a
fixative agent such as an aldehyde (e.g., formaldehyde or
glutaraldehyde) for a fixation time period (e.g., when 0.625%
glutaraldehyde is used as the fixative the time period will be 0.5
hours to 14 days) to effect crosslinking of the connective tissue
proteins within the tissue. [0033] 3. DSC TREATMENT--before or
after performance of the fixation step (Step B above) the
biological tissue is placed in contact with (e.g., immersed in) a
denaturant/surfactant/crosslinking agent (DSC) solution at a
temperature between 4 and 50 degrees C. for a period of time
ranging from 90 minutes to 35 hours). This DSC treatment step is
typically performed before transportation of the biological tissue
into a clean room or aseptic environment, but may additionally or
alternatively be performed at other times such as after assembly of
the bioprosthesis as described in more detail herebelow. [0034] 4.
ASSEMBLY/FABRICATION OF PROSTHESIS--trimming or configuring the
biological tissue (if necessary) and attaching any required
non-biological components (e.g., stents, frames, suture rings,
other hardware elements) thereto. This assembly/fabrication step is
typically performed in a clean room or aseptic environment; [0035]
5. TERMINAL STERILIZATION--subjecting the biological tissue to a
sterilant (e.g., a liquid sterilant such as 0.2-2.0% by weight
glutaraldehyde solution) for a sterilization time period. A 0.625%
glutaraldehyde solution may be used in combination with heat (i.e.
warming above room temperature but below a temperature which would
cause damage to the tissue of the bioprosthesis), as the sterilant.
Alternatively, a suitable sterilant solution may comprise an
osmotically balanced aqueous solution alone or in combination with
a non-contacting source of sterilization (e.g., radiation, electron
beam, UV, or other similar expedient), or include an aqueous
solution of glutaraldehyde in combination with the above-described
DSC mixture or some components of such DSC mixture. In instances
where a 0.625% glutaraldehyde solution is used as the sterilant,
the sterilization time period may be 1-6 days at 37 degrees C. or
1-2 days at 50 degrees C.). This terminal sterilization step may be
performed after packaging of the bioprosthesis in its final
container, thereby eliminating the need for any subsequent handling
of the bioprosthesis until the time of implantation.
[0036] Further in accordance with the invention, there are provided
various types of bioprosthetic articles that are wholly or
partially formed of tissue that has been prepared by the
above-summarized fixation/sterilization method of the present
invention. Examples of specific biological tissues which may be
utilized to prepare bioprosthetic articles in accordance with this
invention include, but are not necessarily limited to: heart
valves; venous valves; blood vessels; ureter; tendon; dura mater;
skin; pericardium; cartilage (e.g., meniscus); ligament; bone,
intestine (e.g., intestinal wall); and periostium.
[0037] Further aspects and objects of the present invention will
become apparent to those skilled in the relevant art, upon reading
and understanding the detailed description of presently preferred
embodiments set forth herebelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a general flow diagram of a
calcification-mitigating treatment method of the present
invention;
[0039] FIG. 2 is a general flow diagram of a treatment method used
as a control in a study of the effectiveness of the present
invention in mitigating calcification;
[0040] FIG. 3 is a general flow diagram of a treatment method used
as a control in a study of the effectiveness of the present
invention in improving hemocompatibility;
[0041] FIG. 4 is a scanning electron microscope image of the
surface of tissue treated in accordance with the method of FIG. 3;
and
[0042] FIG. 5 is a scanning electron microscope image of the
surface of tissue treated in accordance with the method of FIG.
1.
[0043] Additional embodiments and aspects of the invention may
become apparent to those of skill in the art upon reading and
understanding of the detailed description and specific examples set
forth herebelow.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0044] As shown in FIG. 1, the fixation/sterilization method of the
present invention generally comprises six (6) steps as follows:
[0045] Step 1: Harvest/Prepare Biological Tissue
[0046] The desired biological tissue is harvested (i.e., surgically
removed or cut away from its host animal). Thereafter, it is
typically, trimmed or cut to size and washed with sterile water,
balanced salt solution, saline or other suitable washing
solution.
[0047] Step 2: Fixation of Biological Tissue
[0048] The biological tissue is then contacted with a crosslinking
agent, such as an aldehyde (e.g., formaldehyde, glutaraldehyde,
dialdehyde starch), polyglycidyl either (e.g., Denacol 810),
diisocyanates, photooxidation, or carbodiimide(s)) to crosslink the
connective tissue proteins present within the tissue. Due to the
long standing use and experience with glutaraldehyde, a presently
preferred fixative for use in this step is a solution of 0.2-2.0%
by weight glutaraldehyde. For example, the biological tissue may be
immersed in a solution of 0.625% by weight glutaraldehyde buffered
to a pH of approximately 7.4 by a suitable buffer such as a
phosphate buffer, for 0.5 hours to 14 days at 4-37 degrees C.
[0049] Step 3: Treatment With Denaturant/Surfactant/Crosslinking
Agent (DSC Treatment: [0050] a. Before or after fixation of the
tissue in Step 2, the tissue is immersed in or otherwise contacted
with a mixture containing i) a crosslinking agent, ii) a denaturing
agent and iii) a surfactant (i.e., a DSC solution). One preferred
DSC solution is a mixture of i) formaldehyde, ii) ethanol and ii)
surfactant (e.g., Tween 80.TM. surfactant, available from ICI
Americas, Brantford, Ontario). A preferred formulation for the DSC
solution is as follows: [0051] Formaldehyde . . . 0.1-10.0% (more
pref. 4+/-0.4%) by weight [0052] Ethanol . . . 1% to less than 60%
(more pref. 2.2+/-2.2%) by weight [0053] Tween 80 . . . 0.1-5.0%
(more pref. 1.2+/-0.12%) by weight
[0054] The tissue is preferably immersed in the DSC solution for 2
to 24 hours and typically about 9 hours. During this immersion
period, the DSC solution is maintained at a temperature of 4-50
degrees C., and typically about 20-37 degrees C.
[0055] Those skilled in the art will appreciate that various
alternative chemical compounds or solutions may be substituted for
each component of the DSC solution, as follows:
[0056] Potential Alternative Denaturing Agents:
[0057] Alcohols/Solvents: e.g., ethanol, isopropyl alcohol,
acetone, ethers of small alkyl size (methyl, ethyl, propyl,
isopropyl)
[0058] Acidified Ethers: e.g., sulfuric acid/ether mixture
[0059] Ketones: e.g., methyl ethyl ketone (MEK)
[0060] Chlorofluorocarbon Solvents: e.g., Genesolve.TM. (Allied
Signal, Inc., Morristown, N.J.)
[0061] Glycols: glycerol ethylene glycol, polyethylene glycols of
varying molecular weight
[0062] Chaotropic Agents: e.g. urea, guanidine hydrochloride,
guanidine thiocyanate potassium iodide
[0063] High Concentration Salt Solutions: e.g., lithium chloride,
sodium chloride, cesium chloride. [0064] 1. Potential Alternative
Surfactants**: **these surfactant compounds can be used
individually or in mixtures such as deoxycholate/Triton or
commercially-available mixtures such as Micro-80/90.
[0065] Anionic Surfactants: e.g., esters of lauric acid, including
but not limited to sodium laurel sulfate (also called sodium
dodecyl sulfate)
[0066] Alkyl sulfonic acid salts: e.g., 1-decanesulfonic acid
sodium salt
[0067] Non-ionic compounds: e.g., compounds based on the
polyoxyethylene ether structures (including Triton X-100, 114, 405,
N-101 available commercially from Sigma Chemical, St. Louis, Mo.),
and related structures; Pluronic and Tetronic surfactants
(available commercially from BASF Chemicals, Mount Olive, N.J.)
[0068] Alkylated Phenoxypolyethoxy Alcohols: e.g., NP40, Nonidet
P40, Igepal, CA630, hydrolyzed/functionalized animal and plant
compounds including, Tween 80, Tween 20, octyl-derivatives, octyl
b-glucoside, octyl b-thioglucopyranoside, deoxycholate and
derivatives thereof, zwitterionic compounds,
3-([cholamidopropyl]-dimethyl ammonio)-1-propanesulfonate (CHAPS),
3-([cholamidopropyl]-dimethyl ammonio)-2-hydroxy-1-propanesulfonate
(CHAPSO) available from Pierce Biotec Company, Rockford, Ill.
[0069] Potential Alternative Crosslinking Agents:
[0070] Aldehydes: formaldehyde, glutaraldehyde, paraformaldehyde,
glyceraldehyde, glyoxal acetaldehyde or acrolein, dialdehyde
starch
[0071] Epoxides: e.g., any of the various Denacols and their
individual reactive species, including mono, di, tri, and
multi-functionalized epoxides
[0072] Carbodiimides
[0073] Diisocyanates
[0074] Photooxidation
[0075] Step 4. Assembly/Fabrication of Prosthesis
[0076] After completion of Steps 1-3, and irrespective of the order
in which Steps 2 and 3 were performed, the tissue is rinsed with a
suitable rinsing solution such as isotonic saline or 0.625%
glutaraldehyde. Thereafter, the tissue may be transported into a
clean room or aseptic environment, and may be further trimmed or
shaped (if necessary) and attached to or assembled with any
non-biological components (e.g., stents, frames, suture rings,
conduits, segments of polyester mesh to prevent suture
tear-through, etc . . . ) To form the desired implantable
bioprosthetic device. Examples of such assembled bioprosthetic
devices include porcine bioprosthetic heart valves (i.e., the
Carpentier-Edwards.RTM. stented porcine bioprosthesis; Baxter
Healthcare Corporation; Edwards CVS Division, Irvine, Calif.
92714-5686), bovine pericardial heart valve prostheses (e.g.,
Carpentier-Edwards.RTM. Pericardial Bioprosthesis, Baxter
Healthcare Corporation, Edwards CVS Division; Irvine, Calif.
92714-5686), stentless porcine aortic prostheses (e.g.,
Edwards.RTM. PRIMA.quadrature. Stentless Aortic Bioprosthesis,
Baxter Edwards AG, Spierstrasse 5, GH6048, Horn, Switzerland), and
bio-mechanical ventricular assist devices (e.g., the Novacor
N-100PC model; Novacor, Oakland, Calif.).
[0077] Step 5: Treatment With Denaturant/Surfactant/Crosslinking
Agent (DSC Treatment) (Optional)
[0078] Optionally, the DSC treatment described in Step 3 above may
be carried out at this point in the procedure instead of as the
third (3.sup.rd) step of the procedure. Or, if such DSC treatment
has already been performed as the third (3.sup.rd) step of the
procedure, it may be repeated at this point in the procedure (e.g.,
as the fifth (5.sup.th) step of the procedure).
[0079] Step 6: Terminal Sterilization
[0080] The bioprosthesis is immersed in or contacted with a
terminal sterilant and heated for a period of time sufficient to
ensure sterility of the bioprosthesis until the time of
implantation. This terminal sterilization procedure is preferably
carried out in the sealed container or package in which the
bioprosthesis will be shipped and stored until the time of
implantation.
[0081] A preferred terminal sterilant is 0.2-2.0% by weight
glutaraldehyde, and most preferably about 0.25% by weight
glutaraldehyde. Although DSC solution or compounds of the DSC
solution can also be used. The preferred terminal sterilization
time and temperature is 1-6 days at 37.degree. C. or 1-2 days at
50.degree. C.
[0082] Preparation of a Stented Pericardial Valve Bioprosthesis
[0083] The following is an example of the manner in which a stented
pericardial bioprosthetic heart valve may be manufactured in
accordance with the method of the present invention.
[0084] STEP 1: A bovine pericardial sac is obtained from a
slaughterhouse, placed on ice, and transported to the location at
which the bioprosthesis will be manufactured. Thereafter, the
tissue is defatted and trimmed.
[0085] STEP 2: The tissue is washed with sterile isotonic saline
solution and is thereafter immersed in a solution of 0.625% by
weight glutaraldehyde buffered to a pH of approximately 7.4 by a
suitable buffer such as a phosphate buffer, for approximately
thirty minutes at room temperature. This results in crosslinking of
the collagen present within the tissue.
[0086] STEP 3: The tissue is then removed from the fixative
solution used in Step 2 and rinsed thoroughly with an aqueous
solution of 0.625% (by weight) glutaraldehyde. Sometime thereafter,
the DSC Treatment of Step 3 is carried out by immersing the tissue
in DSC solution for 2 hours at ambient temperature. The DSC
solution has the following formula: TABLE-US-00001 2. Formaldehyde
4.0 +/- 0.4% by weight 3. Ethanol 22 +/- 2.2% by weight 4. Tween 80
1.2 +/- 0.12% by weight
[0087] STEP 4: After completion of the DSC Treatment of Step 3, the
tissue is removed from the DSC solution and leaflets are formed.
Thereafter, the leaflets are mounted upon and sutured to a stent.
Also, a needle-penetrable suture ring is attached about the inflow
end of the valve to facilitate suturing of the bioprosthesis to the
native tissue of the host patient. This completes the assembly and
fabrication of the bioprosthetic heart valve.
[0088] STEP 5: Subject the finished valve after inspection to DSC
treatment again for 9 hours at 37.degree. C.
[0089] STEP 6: After the bioprosthesis is removed from the DSC
solution it is transferred to a container which has been pre-filled
with 0.25% glutaraldehyde aqueous solution buffered to a pH of 7.4
with sodium hydroxide such that the bioprosthetic valve is fully
immersed in the buffered glutaraldehyde solution. Thereafter, the
container is sealed and placed in an oven where it is heated to a
terminal sterilization temperature of 37.5+/-2.5 degrees C. for
25-27 hours. Thereafter, the container is cooled to room
temperature and shipped to the hospital or other location(s) where
it is stored until the time of implantation of the bioprosthetic
valve.
[0090] Studies were performed to objectively assess the benefits of
the above-described process in mitigating calcification and
improving hemocompatibility. First, the new process was compared
with a process as shown in FIG. 2, which includes a terminal
sterilization step after "assembly," but does not include any
intermediate DSC steps. The assembly step in this case consisted of
cutting pieces of fixed tissue into circles for subcutaneous
implantation in animals. After a suitable period, the tissues were
explanted and analyzed for calcium content, an indicator of
calcification rate. In a second study, the new process was compared
with a process as shown in FIG. 3, which includes intermediate DSC
steps but does not include a terminal sterilization step. The
resulting tissues were then exposed to whole blood for a period and
the surfaces photographed using a scanning electron microscope to
visibly determine any differences.
[0091] In the first comparison study, control tissues were
generated by traditional glutaraldehyde fixation in conjunction
with a terminal sterilization step as described above. In these
tests, circular pieces of tissue prepared by the new method and by
the control method were surgically placed in either the
subcutaneous space in rats and rabbits, or in a pocket created in
the paravertebral muscle in the rabbit. After thirty days
implantation the tissues were excised from the host tissue, rinsed,
and calcium content is determined by atomic absorption
spectroscopy. The study results are as follows: TABLE-US-00002
Determination of Calcium Content by Atomic Absorption Spectroscopy
Tissues surgically implanted for Thirty days (ug Ca/mg tissue, dry
weight) Implant site: n: Control: n: New process: Rat subcutaneous
6 124.04 .+-. 19.69 6 0.07 .+-. 0.18 Rabbit 6 95.35 .+-. 48.69 6
9.07 .+-. 7.88 subcutaneous Rabbit 5 165.13 .+-. 22.88 4 86.15 .+-.
51.58 intramuscular
[0092] As is apparent, tissue produced according to the new process
demonstrate reduced calcification in rat and rabbit implantation
assays, and demonstrate the superiority of the new tissue
preparation method compared to the control method.
[0093] The second study shows that tissues prepared according to
the new method also demonstrate reduced adhesion of blood cells
compared to a traditional treatment methods. The control method for
the second study is seen in FIG. 3, and includes traditional
glutaraldehyde fixation in conjunction with intermediate DSC steps.
Scanning electron microscopy was used to assess the degree of
adhesion of blood cells after exposure of anticoagulated whole
human blood to tissues prepared according to the new method and to
tissues prepared by the control method of FIG. 3. After a one hour
exposure to whole human blood, the tissues were rinsed, critical
point dried, lightly coated with gold and imaged in the SEI mode at
an accelerating voltage of 5 kV in a JEOL 6300F field emission
scanning electron microscope. The results are shown in FIGS. 4 and
5.
[0094] FIG. 4 shows an image from a representative area on the
control tissues after exposure to whole human blood in vitro. Note
numerous adherent cells and platelets on the surface. FIG. 5 shows
an image from a representative area on tissues prepared by the new
process after exposure to whole human blood in vitro. Note the
nearly complete absence of adherent cells and platelets on the
surface. These images demonstrate the improved hemocompability
(i.e., reduced thrombogenicity) of the material prepared using the
new process compared to the control method.
[0095] The invention has been described hereabove with reference to
certain presently preferred embodiments or examples only, and no
effort has been made to exhaustively describe all possible
embodiments or examples of the invention. Those skilled in the art
will recognize that various modifications, additions and changes
may be made to the particular embodiments and examples described
hereabove without departing from the intended spirit and scope of
the invention. Accordingly, it is intended that all such
modifications, additions and changes be included within the scope
of the following claims.
* * * * *